fixes to grammar

Made editing fixes, grammar, capitalization, etc.
rephrased some sentences that were ambiguous (to me)

Also this statement is not really correct "Gaussian filtering is highly effective in removing Gaussian noise from the image.": the main goal of the Gaussian filter is to attenuate the influence of pixels that are further away from the central pixel, when compared to pixels that are immediately adjacent, and do this 'smoothly', i.e. use filter coefficients that fall off to zero smoothy. The Gaussian effect is in the spatial domain. On the other hand, if you are talking about Gaussian noise, you are talking about the intensity domain. Different things like you explained in the bilateral filter... One of the nice features of Gaussian vs. box filter is that b/c of the abrupt falloff of the box filter coefficient in the spatial domain (effectively the box filter is a step function in 2D) we will get Gibbs effects, therefore aliasing. (indeed the Fourier transform of a step function filter is a sinc function, and the ripples in the sinc are what causes  aliasing). By contrast the Fourier transform of a Gaussian is also a Gaussian, 
therefore no ripples, no Gibbs effects, a nice and clean low pass in the frequency domain..

In sum I would just remove that sentence.

Btw, this tutorial is really a great ressource! Thanks for putting it together and making it available. Awesome work. We are going to use it in our class at JHU and will encourage students to submit back errata.